New M/C, new SS line, fresh piston and seal. The brake worked great for nearly 700 miles this summer then started dragging yesterday. Dragging badly. I borrowed a crescent wrench and bled some fluid off to get home but I wonder what is going on.
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
My disc brake is dragging.
- Thread starter Kevin Werner
- Start date
Usually it's due to water (unlikely) or air in the system. Expands as the dragging bake generates heat so there's positive feedback. Had the front brake on a Buell drag so bad it was almost stopping the bike. Solution was of course bleeding obvious . . .
When you opened the bleeder did you see any air come out?
my
The fact that you could bleed out pressure at the caliper rules out the caliper. That leaves the line or MC.
What I would do is ride it and carry tools to loosen the line at the MC. If you bleed off fluid and it quits dragging then most likely a MC problem. If problem doesn't go away most likely a line problem. Also carry a wrench that fits the bleeder in case it's a line issue.
The fact that you could bleed out pressure at the caliper rules out the caliper. That leaves the line or MC.
What I would do is ride it and carry tools to loosen the line at the MC. If you bleed off fluid and it quits dragging then most likely a MC problem. If problem doesn't go away most likely a line problem. Also carry a wrench that fits the bleeder in case it's a line issue.
New MC my bet is a plugged relief port from bore to reservoir the second TINY port. Been there a bunch of times.
I assume that if I can see the MC piston through the port sliding past the port as I squeeze the brake lever that the port is clear. Am I missing something there?
A rear MC here. but the same deal, not the BIG port you can see through, but the second TINY port. The biggest thing that will fit is the tip of a small needle or fine copper wire. I keep a sharpened piece of safety wire just for this occasion.
We've run into several aftermarket MC's where the hole was not completely drilled through from the factory.
It's tinier than your tiniest drill bit by a lot. Any tiny stray piece of dirt can plug it and the symptom is exactly what you are describing.
It's tinier than your tiniest drill bit by a lot. Any tiny stray piece of dirt can plug it and the symptom is exactly what you are describing.
Called the "compensator port."
If you're using the stock M/C, you can screw the lever adjuster in far enough that the compensating port never -un-ports. Try unscrewing it some?
Unless you're a Harley tech writer? I think both terms are used, I'll toss balance port in there as well.
https://serviceinfo.harley-davidson.com/sip/service/document/1410717547565891826?locale=en_US
Things one finds while wandering around:
In all drum-brake, single cylinder designs, the return spring holds a residual check valve in place to retain a few pounds per square inch of pressure in the hydraulic system.
That petal shaped valve on the end of the piston.
In all drum-brake, single cylinder designs, the return spring holds a residual check valve in place to retain a few pounds per square inch of pressure in the hydraulic system.
That petal shaped valve on the end of the piston.
The "compensator port" is also referred to on boards like this as the spooge hole. The tiniest of particulate matter can plug it up.
replenishing port
Riding cross country on a venture Royal the clutch started slipping a bit, the next day it was fine, then slowly got worse as I rode (Highway not clutching).
Problem was?
Problem was?
spooge hole gummed ??
Poked with a fine piece of wire, except for an eye full of brake fluid (clutch control used DOT4) that squirted out, all good.
Did the full R&R when I got home.
I have an aftermarket 12.7mm MC. The make up port is quite large and clearly open. The reservoir isclean. The caliper moves freely in the carrier and bubbles don't come out (I bled with a section of clear tube),
There will be a second, smaller port in there. The large hole is to allow fluid into the backside of the piston... otherwise there'd be a vacuum behind that would interfere with the piston sealing. You want to find the small one. That's the one that supplies fluid to the caliper.
